As development of rotor spinning machines progresses, the goal is not only to improve the quality of the yarns produced, but above all to increase production capacity. A key factor in increasing production capacity is the rotary speed of the spinning rotor. For this reason, varied kinds of drives and bearings for spinning rotors have been developed, in order to reach rotary speeds of markedly over 100,000 rpm. Reducing the rotor diameter and mass and lowering friction losses enables not only greater rotary speed but also reduced energy consumption when driven.
In this respect, a shaftless spinning rotor, which is embodied as the rotor of an axial field motor, can be considered especially advantageous by providing a combined magnetic and gas bearing which assures relatively low friction losses.
A shaftless open-end spinning rotor of the above-described type having a combined magnetic and gas bearing is known from International PCT Patent Reference WO 92/01097, which discloses a rotor having a bearing face, remote from the spinning chamber of the spinning rotor, and means for conducting the magnetic flux for the driving and guiding magnetic fields. By means of the guiding magnetic field, the rotational axis of the open-end spinning rotor is to be rigidly defined and maintained during rotation. However, it has been found impossible to achieve significant suppression of impermissible vibratory, wobbling and oscillating motions that occur particularly in critical rpm ranges. Moreover in the central region of the stator of the axial field motor, overheating tends to occur which causes thermal expansion and can ultimately lead to problematic warping.